1. Field of the Invention
This invention relates to water-soluble cellulose ethers containing alkenyl and/or alkyl succinic acid ester moieties which are capable of forming highly viscous aqueous solutions.
2. State of Related Art
U.S. Pat. No. 2,661,349 describes a process for the production of water-soluble derivatives of cellulose or starch which comprises a substitution with long-chain dicarboxylic acid anhydrides, such as alkenyl succinic acid anhydride. The patent specification describes (1) a method in aqueous medium, (2) a solvent-free method (called dry method), and (3) a method in suspension in organic solvents. In every case, however, the presence of water is either required or is not ruled out and an alkaline range, established by an excess of sodium carbonate for example, is compulsory. If this method is applied to water-soluble cellulose derivatives, particularly in aqueous phase, no reaction of the alkenyl succinic acid anhydride is observed.